Protecting device for electric detonators



D. D. HUYETT July 1, 1941.

- IROTECTING DEVICE FOR ELECTRIC DETONATORS Filed may 28, 195s Y Patented July l, 1941 PATENT. OFFICE rno'rEc'r-nva DEVICE Fon ELECTRIC i nE'roNA'rons Daniel Il). Huyett.' Wilmington, Del., assignor to Atlas Powder Company, Wilmington, Del., a`

corporation of Delaware Application May 28, 1938, Serial No. 210,564

ZCIaims.

This invention relates to a protecting device for electric detonators, and more particularly t the type of protecting applied to the uninsulated portion of the lead-in wires of electric detonators and generally referred to as a shunt. o

An object of the invention is to provide a protecting device which will more surely guard against the l detonator beingv prematurely exploded should its lead-inwires accidently contact a source of electricity.

' A still further object of the invention is the provision of a protective shunt which may be pressed ilrmly upon the lead-in wires of the detonator without injuring them, but which may be readily removed from the wires when it is desired to connect the wires for ilring the shot.

Other objects of the invention will hereinafter more fully appear.

Figure 1 is an elevation of an electric detonator and its lead-in wires having the protecting device of the present invention applied thereto. y

Figure 2 is a seflo'naLNiew on line 2-2 of Figure 1.

Like numerals designate corresponding parts in both of the ilgures of the drawing.

Referring to the drawing, 'l designates the casing of an electric detonator and 3 and I the insulated lead-in wires, usually of copper or iron wire, which extend from the casing. Within the detonator, the lead-in wires are attachedto an igniting element l8, and at the outer end the lead-in .wires have uninsulated portions la and la, which may be readily attached tn a source of electricity. In the ordinary use of such a dewnatur; now of sufilcient current through the igniting elemen't l explodes the detonator.

To prevent premature iiring of the detonator by stray currents, a protecting device or shunt l is applied tothe lead-in wiresat a point closely adjacent the termination of the insulation. ,As long as this shunt is inplace', current accidently applied `to the uninsulated portions la and la'of lead-in wires will short-circuit through the shunti and premature firing of the igniting element l is thereby prevented. p j Heretofore, in protecting devices-of this character, dimculty has been had in securing good contact between the shunt andthe lead-in wires to assure short-circuit without subjecting the m lead-in wires to injury upon applicationror rel moval of the shunt. When relatively soft metals such as lead were employed tol obtain'good contact with uninsulated portionsv of the lead-ln "fwires.' it was found that upon.applicaticn of 55 heavy currentsv to the outer endsof the lead-in wires, the relatively soft metal would frequently v melt and fall away from the wires,thereby permitting current to go through the igniting element and explode the cap. On the other hand. where relatively hard metals of high melting point were employed for shunt purposes and compressed about thewires with force insulcient to injure the wires, poor contact frequently resulted, thereby increasing the resistance across the shunt. 'This increased resistance resulted in a greater proportion of the current passingthrough the illament and frequently inthe explosion of the detonator.

In accordance with lthe present invention, lthe shunt or protecting device is made of laminated material having a layer of soft metal of low melting point, such as lead, tin or lead-tin alloy, adjacent to and in contact with the lead-inwires A and an outer layer of relatively hard metal 'of relatively high melting point. 'I'he metal of the outer layer has a hardness and melting point not less .than that of annealed or soft temper 99% plus pure, aluminum striV sheet, of Brinell hardness 23 500v kg., and ltlng point of about 1215 F. Suitable metals for the outer layer are. for example,v aluminum, silver.y copper. bronze, brass, iron and steel. Various alloys of the required hardness andmelting point'may' be employed as the outer layer. Preferably. the outer layer of metal is of sufilcient'strength andv toughness to withstand bending 180l without fracturing or weakening, and is of low` remilene so that the shunt may be bent about andpre'ssed upon the lead-in wires, and will thereafter remain tight and not tend to spring oil. Materials having the required properties for the outer layer of the shunt, and which at the same time are ...readily ladaptable to the,..shunt fabrication operations usually employed, are aluminum. copper, soft steel and certain of the copperFbase-alloys. y v

In the embodiment of the invention showngin rig. a of the drawing, the shunt l is intne'rcrm of a strip of laminated material electrically connecting and partially embracing an uninsulatcd portion o f each ofthe lead-in wires. The 18minated material has an outer layer I of metal havinga hardness and melting point not less than *I that of aluminum, as for example, copper and en inner layer 'I -of relatively soft'metal of relitti"- ly low melting point, such as lead, tin onloadtin alloy.-

The two wires are locatedclose together well 2 l backr near the bend of me metal and me mad Y surfaces are pressed tightly together forming an excellent contact with the wires. Though pressed tightlyupon the wires, the relatively softl metal doesY not injure the wires and renders the shunt readily removable from the wires without inJury thereto.

When heavy current is applied to' the outerends of the lead-in wires and the current is of.

sumcient strength to melt the inner layer of soit metal, the outer, protective layer of metal of. relatively high melting point. holds sufiicient` molten metal in contact with the wires to maintain the short-circuit... The melting of the inner layer tends to increase the degree of contact of the shunt with the wires, and at least a portion of the molten metal appears to -be held in `the crevices adjacent the lines of contact of the wires and shunt by capillary attraction, as' the molten metal tends to be retained in contact with thel wires in sufiicient quantity to maintain the shortcircuit even though the wires be moved.

Repeated tests oi.' copper-lead laminated protecting devices embodying the present invention 'by subjecting` the outer ends of copper lead-in 'soft layer oi' lead, lead-tin alloy, or the lilre.

bonded to the relatively hard, high melting point material, such as copper, bronze, iron or steel. Such bonding may be accomplished by tin-plating the copper, bronze, iron or steel, and thereafter rolling lead on the tin-plated surface under* heat and pressure. so that alead-tin alloy is formed at the jointure of the two metals.. thereby bonding them together. When such bonded, laminated material is employed, and the shunt is subjected to current density suilicient to melt the' inner layer of relatively soft metal, good wetting invention is not to be considered as limited in this respect as the protective device can be in other form such as a tubular, laminated body through which the bare portions of the wires are threaded and which body has been compressed about the wires, so long as the lamination is such that the relatively soit metal of relatively low melting point is adjacent -to and in contact with the wires.

Other modifications will be apparent to those familiar with the art.

Having described my invention, what I claim is as follows:

1. In a detonator assembly having a detonator and lead wires therefor; a shunt for electrically contact at the surface interfaceb'etween the two metals is assured, thereby aiding the capillary attraction and increased degree of contact described above. A laminated material formed by sweating a .015" layer of lead to a tinned copper layer of about .015" has been found to be excellently suited for the production of a protective device employed on 20 to 22 gauge lead-in wires. It is connecting an uninsulated portion of each of the wires and adapted to be readily removed there-- from, said shunt comprising a Astrip of laminated metal dimensioned and bent so that when positioned vupon nninsulated portions of the lead wires and pressed thereon, said lead wire portions are embraced in substantially parallel relation near the bend in the strip, said laminated metal having a first inner. layer adapted to be in contacting engagement with'the wires and consisting essentialiy of metal taken fromgroup consisting of lead and tin, and a second layer of metal exteriorly positioned with respect to said first layer and adapted to be separated from said wires by means ofA said iirstrlayer, said second layer of metal having a hardness and melting point not less than that of aluminum, ,said shunt being 'so constructedfthat when4 pressed upon the lead wires thefsecond layer of metal is'close enough thereto so that upon melting of the inner layer of metal due to the application of current to the wires, a quantity of-molten Vmetal of the inner layersumcientto maintain the eiectr'lcaleonnle'c-v non across the wim wur be retained in contact" with the wires.

2. A shunt for detonator lead forth in claim i and `wherein vthe 'nrst layer is bonded to the second layer by means oi a lead-tin alloy. I l Y Y! DANIEL wires asset. 

